JP3294404B2 - How to treat incinerator dust - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating soot and dust in an incinerator for municipal waste and industrial waste.

[0002]

2. Description of the Related Art In addition to carbon dioxide, steam, nitrogen and oxygen, the exhaust gas of the incinerator contains soot, hydrogen chloride, sulfur oxides, nitrogen oxides and heavy metal compounds. Since these substances cannot be discharged, it is necessary to remove these substances contained in the exhaust gas. Conventionally, in the exhaust gas of an incinerator, for example, harmful gas is reacted and removed according to a process shown in a flow sheet of FIG.
Soot containing heavy metals contained in exhaust gas has been solidified with cement or the like or subjected to chemical treatment, and then finally disposed of. This soot and dust has been designated as a specially managed waste by the "Waste Disposal and Public Cleansing Law" (revised in October 1991).

Referring to FIG. 2, the high-temperature exhaust gas generated from the incinerator body 21 is discharged from a waste heat boiler 22.
In the cooling tower 23.
The cooling exhaust gas separates soot and dust with a dust collecting device 24, is attracted by an induction blower 25, and is discharged from a chimney 26. On the other hand, the separated dust is temporarily stored in a dust storage tank 28 by the conveyors 27 and 29, and is supplied to the mixer 30 quantitatively. Water (supply tank 33), pH adjuster (supply tank 34),
A solidifying agent and / or a chemical (supply tank 35) are added, kneaded, and, if necessary, formed and stored in the pit 32. During the process, in order to remove harmful gases such as hydrogen chloride and sulfur oxide, slaked lime (supply tank 36, transport blower 37) is blown and mixed into the flue upstream of the dust collecting device 24 as in this example. Or install a cooling reaction tower to introduce exhaust gas,
Methods such as spraying an alkaline slurry such as slaked lime are being implemented. The composition of the exhaust gas varies depending on the composition of the incinerated material, the type of furnace, the operation method, and the like. Therefore, the removal rate required to keep the concentration of hydrogen chloride or the like below the allowable value is not uniform. However, in general, for example, 300-800p
In order to reduce the pm hydrogen chloride removal rate to 40 to 80%, it is necessary to mix an excess of slaked lime, which is about twice the equivalent, into the exhaust gas.

[0004]

By the way, heavy metals such as lead, cadmium, chromium and mercury are usually present in the separated soot, but the soot and dust contain excessive amounts It contains an alkaline agent and a reaction product, has a high pH, and contains many heavy metals,
Even if soot is treated and finally disposed, there is little risk of elution. However, with respect to amphoteric heavy metals such as lead, there is a problem that elution is accelerated when pH is high. Therefore, to prevent the elution of lead etc., the pH of the dust was adjusted by adding a pH adjuster.However, conventionally, the pH of the dust once stored in the dust storage tank was measured, and the fixed ratio of the pH adjuster was determined. Therefore, the adjustment effect was not certain. The present invention has been completed for the purpose of improving the method of adding a pH adjuster, and providing an effective and economical method for treating particulate matter in which amphoteric metals such as lead do not elute.

[0005]

According to the present invention, there is provided a method for treating incinerator soot and dust.
While separate narrowing blow an alkaline agent in the exhaust gas to react with acidic noxious gases in the exhaust gas, a dust containing the resulting reaction product and residual alkaline agent in dust collector, A
Detecting the injection equivalent of lukari agent and detecting the p
Provided is a method for treating incinerator dust, characterized by adding a pH adjuster to separated dust so that H is maintained in a range of 8.5 to 11.5. The present invention
In the above-mentioned method for treating incinerator dust , powdered p
After the addition from the dust collector 4 to the dust storage tank 8 using the H adjuster , water and a solidifying agent and / or a chemical are further added and mixed, and the pH adjuster is replaced with water and the solidifying agent.
And / or mixing taking into account pH fluctuations due to mixing of drugs.
The pH of the dust after the combination is maintained in the range of 8.5 to 11.5
Incinerator soot and dust added
Is provided.

[0006]

The present invention will be specifically described with reference to a flow sheet showing an example of an apparatus for practicing the present invention in FIG. This embodiment is an example in which, based on the conventional exhaust gas treatment process exemplified in FIG. 2 described above, the process is improved to a process that can utilize the method for treating incinerator soot and dust of the present invention. Exhaust gas generated from the incinerator body 1 is recovered by the waste heat boiler 2 and further cooled in the cooling tower 3 to usually 250 ° C. or less. Since harmful gases such as hydrogen chloride and sulfur oxides are contained in the cooled exhaust gas, an excess of an alkali agent, for example, slaked lime (Ca (OH) ₂ ) is blown into the exhaust gas to produce these harmful gases. And removed as a solid reaction product. In addition to the present embodiment examples, a cooling reaction tower is provided to introduce exhaust gas, and an alkali agent slurry is sprayed from a nozzle or a special atomizer to contact the exhaust gas,
The exhaust gas can be cooled by the heat of evaporation of the slurry and, at the same time, can be reacted with the acid gas in the exhaust gas. The reaction product is
It becomes a powder solid.

The amount of the alkaline agent to be blown is usually measured by measuring the concentration of hydrogen chloride in the exhaust gas at the inlet of the chimney 6 as in this embodiment, and controlling the amount of the alkaline agent to be fed back. Slaked lime or the like is often used as the alkaline agent. The exhaust gas that has been cooled and from which harmful acidic gases have been removed is led to a dust collecting device 4, where it separates the dust containing the reaction product and the residual alkali agent, and is attracted by an induction blower 5,
It is discharged from the chimney 6 to the outside. As the dust collecting device 4, an electric dust collector, a bag filter, or the like can be used.

On the other hand, the soot and the like separated in the dust collecting device 4 are in a powder form and are usually finally disposed after solidification and / or chemical treatment with cement or the like to fix heavy metals. In the present embodiment, the relationship between the blowing equivalent of the alkaline agent and the pH of the dust is grasped, and the pH adjusting agent of the powder is supplied from the pH adjusting agent supply tank 14 to the dust during transportation by the conveyor 7 by the blowing equivalent of the alkaline agent. Add with control and mix well. The soot mixed with the pH adjuster is stored in a soot storage tank 8 and then supplied to the kneading machine 10 quantitatively. Water is supplied from the supply tank 13, a solidifying agent or a chemical is added from the supply tank 15, and then kneaded. Can be stored.

Examples of the pH adjuster include aluminum sulfate (solution, powder), ferric chloride and the like. Ferric chloride has a problem in safety. Aluminum sulfate is preferably used. The amount of the pH adjuster added is determined by detecting the equivalent of the injected alkaline agent, taking into account pH fluctuations due to the addition of a solidifying agent and / or chemicals, if necessary, And so on so that the amphoteric heavy metals do not elute. Incidentally, Table 1 shows examples of the measurement results of the relationship between the pH of various types of incinerator dust and the amount of lead eluted.

[0010]

Table 1 Sample ABCD pH 10.2 12.0 11.9 10.2 Eluted lead (mg / l) ^* 0.12 73 73 0.08 (Note) Measurement method: Included in industrial waste In accordance with the test method for metals, etc. (Environment No. 13).

In the present invention, the pH of the dust after the treatment is adjusted to a range of 8.5 to 11.5, preferably 9 to 11. It is not always necessary to directly detect the amount of the alkaline agent to be blown, and for example, the control value of the above-mentioned alkaline agent to be blown may be known. Then, the amount of the pH adjuster added is determined in advance by determining the correlation between the equivalent of the blowing of the alkaline agent and the pH of the dust, and using, for example, a microcomputer to set the appropriate pH.
What is necessary is just to calculate and control the addition amount of the adjusting agent. If necessary, the solidifying agent to be added and the pH of the dust after the treatment
The relationship with can also be incorporated. Cement or the like is used as a solidifying agent, and a heavy metal fixing agent or the like is used as a chemical.

[0012]

By using the method for treating incinerator soot and dust according to the present invention, a pH adjuster conventionally added in a fixed manner can be added without waste in an amount corresponding to the equivalent amount of the alkali agent to be blown. The pH of the soot and dust after the treatment can be maintained in a range in which heavy metals such as lead do not elute. Moreover,
In the present invention, since the addition amount of the pH adjuster is controlled in a feedforward manner, the timing of addition can be appropriately selected, and the pH of the soot and dust after the treatment can be reliably controlled within a desired range. .

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an example of an apparatus for implementing the present invention.

FIG. 2 is a flow sheet showing an example of a conventional exhaust gas treatment process.

[Explanation of symbols]

1,21: Incinerator body 2,22: Waste heat boiler 3,23: Cooling tower 4,24: Dust collector 5,2
5: Induced blower 6, 26: Chimney 7: Pneumatic transport pipe 27: Conveyor 8, 28: Dust storage tank 9, 29: Conveyor 10, 30: Consolidation molding machine 11, 31: Conveyor
12, 32: pit 13, 33: water supply tank 14, 34: pH adjusting agent supply tank 15, 35: solidifying agent supply tank 16: blower 17:
Slaked lime supply tank 18: Blower 36: Slaked lime supply tank 37: Blower

Claims (2)

(57) [Claims] In the processing method according to claim 1] incinerator dust, soot and dust collector including narrowing blow an alkali agent in the exhaust gas to react with acidic noxious gases in the exhaust gas, the the resulting reaction product and residual alkaline agent While separating
Detecting the equivalent of the blowing agent, and adding a pH adjuster to the separated dust so that the pH of the separated dust is maintained in a range of 8.5 to 11.5.
How to treat incinerator soot and dust. 2. A method for treating the incinerator soot and dust according to claim 1.
In law, the dust separated from the exhaust gas, pH
After using a pH adjuster in powder form as the adjuster and adding it between the dust collector (4) and the dust storage tank (8) , water, a solidifying agent and / or a chemical are further added and mixed .
First, a pH adjuster is mixed with water and a solidifying agent and / or a drug.
The pH of the dust after mixing is
8.5 to 11.5.
And a method for treating incinerator soot and dust.